Multilayered composite

ABSTRACT

In accordance with certain embodiments of the present disclosure, a process for forming a multilayered electrospun composite is provided. The process includes forming a dispersion of polymeric nanofibers, a fiberizing polymer, and a solvent, the dispersion having a viscosity of at least about 50,000 cPs. Nanofibers from the dispersion are electrospun onto a first ePTFE layer. A second ePTFE layer is applied onto the nanofibers to form a composite structure. The composite structure is heated.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation application of U.S.application Ser. No. 13/564,925, filed Aug. 2, 2012; which applicationis a continuation application of U.S. application Ser. No. 12/852,989,filed Aug. 9, 2010, now U.S. Pat. No. 8,257,640, issued Sep. 4, 2012;which application claims priority to U.S. Provisional Application Ser.No. 61/232,252, filed Aug. 7, 2009; all of which are incorporated byreference.

BACKGROUND

Electrostatic spinning of polytetrafluoroethylene (PTFE) into continuousfiber allows for the formation of non-woven sheets, tubes, and coatingswith potential for multiple other applications and forms. The process ofelectrostatic spinning is well known in the literature and the patentureas represented by U.S. Pat. Nos. 2,158,416; 4,432,916; 4,287,139;4,143,196; 4,043,331; 4,689,186 and 6,641,773 each of which isincorporated herein by reference thereto. While most of these patentspertain to soluble polymers or thermoplastics, none pertain directly tothe formation of fibers or mat from virtually insoluble polymers orthose that do not flow readily on heating to elevated temperatures. Areview of the literature and patenture revealed limited reference to theprocess whereby a polymer that meets the properties of limitedsolubility and inability to readily flow upon heating such as PTFE canbe formed into a fiber suitable for electrostatic spinning into variousstructures. U.S. Pat. Nos. 4,323,525 and 4,044,404, both of which areincorporated herein by reference, provide information related toprocessing and electrostatic spinning of PTFE from an aqueous or otherdispersion.

However, such conventional processes have several shortcomings. Suchprocesses describe the use of low viscosity PTFE dispersions (15,000cPs) which do not result in uniform or consistent fiber formation.Furthermore, such processes describe the use of a grounded spinning headand a charged target. Observation shows various levels of degradation insamples produced by reverse polarity. Conventional processes also failto accommodate for shrinkage of a mat during sintering.

Thus, a need exists for processes that address the deficienciesdescribed above. Materials made from such processes would also beparticularly beneficial.

SUMMARY

In accordance with certain embodiments of the present disclosure, aprocess for forming a multilayered electrospun composite is provided.The process includes forming a dispersion of polymeric nanofibers, afiberizing polymer, and a solvent, the dispersion having a viscosity ofat least about 50,000 cPs. Nanofibers from the dispersion areelectrospun onto a first ePTFE layer. A second ePTFE layer is appliedonto the nanofibers to form a composite structure. The compositestructure is heated.

In other embodiments of the present disclosure, a process for forming amultilayered electrospun composite structure is disclosed. The processincludes electrospinning a dispersion having a viscosity of at leastabout 50,000 cPs and comprising polymeric nanofibers, a fiberizingpolymer, and a solvent, onto a first side of an ePTFE layer. The processfurther includes electrospinning a dispersion having a viscosity of atleast about 50,000 cPs and comprising polymeric nanofibers, a fiberizingpolymer, and a solvent, onto a second side of the ePTFE layer to form acomposite structure. The composite structure is heated.

In still other embodiments of the present disclosure, a process forforming a multilayered electrospun composite structure is described. Theprocess includes forming a dispersion of polymeric nanofibers, afiberizing polymer, and a solvent, the dispersion having a viscosity ofat least about 50,000 cPs. Nanofibers from the dispersion areelectrospun onto a first ePTFE layer. A substrate is applied onto thenanofibers to form a composite structure. The composite structure isheated.

Through diligent research the inventors have determined that electrospunmaterials, such as PTFE, when applied to ePTFE membranes constitutes anadditional application, form, and use of electrospun materials.Furthermore, the inventors have determined that a wide range ofelectrospun materials when combined in layers with ePTFE membranesand/or other substrates can create composite membrane structures withnew and unique properties.

Other features and aspects of the present disclosure are discussed ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure, including the best mode thereof,directed to one of ordinary skill in the art, is set forth moreparticularly in the remainder of the specification, which makesreference to the appended figures in which:

FIG. 1 illustrates an SEM image of a multilayered composite constructionin accordance with the present disclosure; and

FIGS. 2-5 illustrate cross-sectional views of different multilayeredcomposites in accordance with the present disclosure.

DETAILED DESCRIPTION

Reference now will be made in detail to various embodiments of thedisclosure, one or more examples of which are set forth below. Eachexample is provided by way of explanation of the disclosure, notlimitation of the disclosure. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present disclosure without departing from the scope or spirit ofthe disclosure. For instance, features illustrated or described as partof one embodiment, can be used on another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present disclosurecovers such modifications and variations as come within the scope of theappended claims and their equivalents.

The present invention is related to multilayered composites comprisingone or more electrospun (also referred to herein as “espin” and/or“espun” and/or “espinning”) membranes attached to one or more expandedpolytetrafluoroethylene (also referred to herein as “ePTFE”) membranes.In certain embodiments, the espin membranes can includepolytetrafluoroethylene (also referred to herein as “espin PTFE”),however, many other suitable materials can be espun and used in additionto or in combination with such espin PTFE. For example, other suitablematerials that can be espun in accordance with the present disclosureinclude nylons, polyurethanes (PU), polyesters, fluorinated ethylenepropylene (FEP), or the like. Polymers that can be placed in a solutionhave the potential to be espun. Polymer particles that can be made intodispersions (such as, PTFE, FEP, and the like) also have the potentialto be espun. The dispersions (espun PTFE) must be sintered to developthe desired properties, but many polymers espun from solution developtheir properties during spinning and drying. The attachment of the espinlayer(s) can occur during sintering.

For example, in certain embodiments the high molecular weight of thepolytetrafluoroethylene that is present in the espin PTFE layer and theePTFE layer melts at the sintering temperatures, but does not flow.Thus, PTFE present in each of the layers has an opportunity to formphysical bonding between adjacent layers. Compression of the layers toforce more intimate contact is advantageous. The multi-layered compositeis particularly useful in medical, industrial, filtration, military andconsumer applications.

A particularly preferred ePTFE is an air permeable expanded membrane. Amembrane which is exemplary for demonstrating the invention is describedin U.S. Pat. No. 4,902,423 which is incorporated herein by reference.Another exemplary membrane is described in U.S. Pat. No. 3,962,152 whichis incorporated herein by reference.

Numerous configurations are contemplated in accordance with the presentdisclosure. For instance, the construction can be a two layer ormultiple layer composite of the materials described herein.

Referring to FIG. 2, a cross-section of a multilayer composite inaccordance with the present disclosure is illustrated. The compositeincludes an ePTFE layer 1 and an espin layer 2. FIG. 1 illustrates anSEM image of such a multilayered composite in which the espin layer isespin PTFE. Advantages of such a configuration include an asymmetricalflow structure because pore size can be controlled. In addition, thepresence of the espin material can result in improved adhesion of thecomposite to subsequent layers. Importantly, the espin material can alsoresult in modification of the ePTFE surface properties.

Turning to FIG. 3, another cross-section of a multilayer composite inaccordance with the present disclosure is illustrated. The compositeincludes an ePTFE layer 1, an espin layer 2, and an ePTFE layer 1. Theespin layer 2 is sandwiched between the ePTFE layers 1. Such aconfiguration allows the mechanical properties of the composite to bemodified, as desired. For example, material recovery can be improvedafter compression. The espin material selection can be adjusted toimprove bonding properties between layers. In this regard, any espunmaterial that has adhesive potential can act to bond layers together.Espun PTFE can act to bond the ePTFE layers together. Espun PU can alsobond ePTFE layers together. In certain embodiments, espun PTFE must beheated to 385° C. to develop bonding characteristics while materialssuch as PU can create a bonding situation at much lower temperatures.

In yet another embodiment of the present disclosure, a cross-sectionalview of an espin layer 2, an ePTFE layer 1, and an espin layer 2 areillustrated as FIG. 4. The ePTFE layer 1 is sandwiched between the espinlayers 2. Advantages of such a construction include modulation ofsurface properties through the espin layer including a) better adhesionto the composite construction if desired, b) changing the surfacefunctionality of the composite, c) manipulation of cellular in-growthand response, and d) increased porosity for improved ingress of othermaterials.

FIG. 5 illustrates yet another embodiment of a cross-section of amultilayer composite construction in accordance with the presentdisclosure. The composite includes a substrate layer 3, an espin layer2, and an ePTFE layer 1. The substrate layer can include woven andnonwoven fabrics of natural or man-made fibers, plastic or ceramicmembranes, metal, ceramic, and plastic meshes, or the like. Forinstance, metal stents are a type of metal mesh. Such a constructionallows for a structure which has increased robustness and durability,while maintaining porosity, air permeability and other desiredproperties of porous materials. The composite can be thermally oradhesively bonded to other woven or nonwoven porous substrates. Such acomposite also results in improved pore size distribution and improveddurability, which can be very beneficial in filtration applicationswhere debris and particulate are contacting the media surface at highvelocities. In addition, the overall filtration efficiency can beimproved as a result of the microstructure of the espin fiberentanglement.

The electrospun layer is preferably applied directly to the membranethrough electrospinning methods understood by those skilled in the art;however, it could also be applied using mechanical nips or lamination aswell. These latter techniques include pressing an electrospun layer ontoa second material layer and heating to a complimentary temperature. Thepressing technique may use a flat press or mechanical nip roller.

The properties and characteristics are a compilation of both a non-wovenand a membrane. The composite can be prepared with controlled fiber,node and fibril sizes and manipulated mechanical values such as bondstrength, elongation properties and tensile strengths.

The properties and characteristics of the composite can be a compilationof the individual properties of the substrate layer, espin layer, andthe ePTFE layers. The composite can be prepared with controlled fiber,node and fibril sizes and manipulated mechanically, such as to improvebond strength, elongation properties and tensile strengths, in the finalcomposite.

Typical construction of multiple layers may produce thickness rangingfrom about 0.0001 inches to about 0.25 inches overall thicknesses atwidths of about 0.032 inches to about 80 inches. The individual layerscan have a thickness that varies from about 0.0001 inches to about 0.25inches. Final material size varies greatly as the composites can beproduced as sheets or tubes at continuous roll lengths. The compositeinternodal distance (IND) can be about 0.1 to about 200 μm with porosityranging from about 20 to 90%. Pore structure as defined by ASTM F316,incorporated by reference herein, can range from about 0.05 to about 50μm. Due to the construction of the composites, the IND, pore size andporosity can vary from layer to layer, within the cross section of thecomposite, depending on the construction. An example would be anasymmetrical construction where pores change in size from large to smallbased on layer evaluations from surface to surface throughout the media.

In certain embodiments of the present disclosure, the process canrequire a dispersion or suspension of PTFE solids between about 10 to85% by weight to aid in the processing of the collected fibrous mat intoa form that has sufficient green strength. However, as described above,other suitable polymers can be utilized for the espin dispersion. If thesolid content in the dispersion is too low, there will be no, or poor,mechanical integrity to the resulting material. Second, the selection ofthe polymer used to increase the viscosity of the solution, suspensionor dispersion to be spun must be selected carefully.

Additionally, when sintering or bonding espin layers it is necessary toinsure that temperatures are selected to properly sinter the material,such that the resulting product has good mechanical integrity.

To produce a non-woven espin PTFE material, a narrow particle sizedistribution PTFE powder is provided in an aqueous dispersion. Theparticle size would preferably be about 0.05 to 0.8μ. About 1 to 10 wt %by weight of a fiberizing polymer is added to the volume of PTFE aqueousdispersion. The fiberizing polymer should have a high solubility inwater with a solubility of greater than about 0.5 wt % being preferred.It is preferable that the fiberizing polymer has an ash content of lessthan about 5 wt %, when sintered at about 400° C., with even lower beingmore preferred. Without limit thereto, particularly preferred fiberizingpolymers can include dextran, alginates, chitosan, guar gum compounds,starch, polyvinylpyridine compounds, cellulosic compounds, celluloseether, hydrolyzed polyacrylamides, polyacrylates, polycarboxylates,polyvinyl alcohol, polyethylene oxide, polyethylene glycol, polyethyleneimine, polyvinylpyrrolidone, polylactic acid, polymethacrylic acidpolyitaconic acid, poly 2-hydoxyelthyl acrylate, poly2-dimethylaminoethyl methacrylate-co-acrylamide, polyn-isopropylacrylamide, poly 2-acrylamido-2-methyl-1-propanesulfonicacid, poly(methoxyethylene), poly(vinyl alcohol), poly(vinyl alcohol)12% acetyl, poly(2,4-dimethyl-6-triazinylethylene),poly(3-morpholinylethylene), poly(N-1,2,4-triazolyethylene), poly(vinylsulfoxide), poly(vinyl amine), poly(N-vinyl pyrrolidone-co-vinylacetate), poly(g-glutamic acid), poly(N-propanoyliminoethylene),poly(4-amino-sulfo-aniline),poly[N-(p-sulphophenyl)amino-3-hydroxymethyl-1,4-phenyleneimino-1,4-phenylene)],isopropyl cellulose, hydroxyethyl, hydroxylpropyl cellulose, celluloseacetate, cellulose nitrate, alginic ammonium salts, i-carrageenan,N-[(3′-hydroxy-2′,3′-dicarboxy)ethyl]chitosan, konjac glocomannan,pullulan, xanthan gum, poly(allyammonium chloride), poly(allyammoniumphosphate), poly(diallydimethylammonium chloride),poly(benzyltrimethylammonium chloride),poly(dimethyldodecyl(2-acrylamidoethyly) ammonium bromide),poly(4-N-butylpyridiniumethylene iodine),poly(2-N-methylpridiniummethylene iodine), poly(Nmethylpryidinium-2,5-diylethenylene), polyethylene glycol polymers andcopolymers, cellulose ethyl ether, cellulose ethyl hydroxyethyl ether,cellulose methyl hydroxyethyl ether, poly(1-glycerol methacrylate),poly(-ethyl-2-oxazoline), poly(2-hydroxyethyl methacrylate/methacrylicacid) 90:10, poly(2-hydroxypropyl methacrylate),poly(2-methacryloxyethyltrimethylammonium bromide),poly(-vinyl-1-methylpyridinium bromide), poly(2-vinylpyridine N-oxide),poly(2-vinylpyridine),poly(-chloro-2-hydroxypropyl-2-methacryloxyethyldimethylammoniumchloride), poly(4-vinylpyridine N-oxide), poly(4-vinylpyridine),poly(acrylamide/2-methacryloxyethyltrimethylammonium bromide) 80:20,poly(acrylamide/acrylic acid), poly(allylamine hydrochloride),poly(butadiene/maleic acid), poly(diallyldimethylammonium chloride),poly(ethyl acrylate/acrylic acid), poly(ethylene glycol) bis(2-aminoethyl), poly(ethylene glycol) monomethyl ether, poly(ethyleneglycol)-bisphenol A diglycidyl ether adduct, poly(ethyleneoxide-b-propylene oxide), poly(ethylene/acrylic acid) 92:8,poly(1-lysine hydrobromide), poly(l-lysine hydrobromide), poly(maleicacid), poly(n-butyl acrylate/2-methacryloxyethyltrimethylammoniumbromide), poly(N-iso-propylacrylamide),poly(N-vinylpyrrolidone/2-dimethylaminoethyl methacrylate), dimethylsulfatequaternary, poly(N-vinylpyrrolidone/vinyl acetate),poly(oxyethylene) sorbitan monolaurate (Tween 20®), poly(styrenesulfonicacid), poly(vinyl alcohol), N-methyl-4(4′-formylstyryl)pyridinium,methosulfate acetal, poly(vinyl methyl ether), poly(vinylamine)hydrochloride, poly(vinylphosphonic acid), poly(vinylsulfonic acid)sodium salt, polyaniline, and combinations thereof. Again, however, suchfiberizing polymers are also contemplated for use with other polymerespin dispersions.

A particularly preferred fiberizing polymer is polyethylene oxide with amolecular weight between about 50,000 to 4,000,000 amupolyethyleneoxide. After mixing, the PTFE and fiberizing polymerdispersion is preferably allowed to homogenize. In a particularlypreferred method the polymer solution is allowed to form slowly, withoutagitation, followed by transfer to a jar roller that will turn it at aconstant rate for several more days. The present disclosure contemplatesthe use of dispersions of greater than 50,000 cPs to provide for moreuniform and consistent fiber formation as well as faster builds. It ispreferred to create a uniform solution that has little to no air trappedin the resulting highly viscous mixture. Once the dispersion is ofuniform consistency it is preferably filtered to remove any clumps orgels. The filtered dispersion with the desired viscosity is then loaded,in a controlled pumping device with a fixed conductive element whichacts as the charge source.

A particularly preferred conductive element is one with one or severalorifices. The orifice size is preferably, but not limited to, about 0.01to 3.0 mm in diameter. The ejection volume from the pumping device isset to a predetermined rate that is dependent on the form being made andthe desired fiber diameters. The charge source is preferably connectedto the positive side of a precision DC power supply. The negative sideof the power supply is preferably connected to the collection surface ortarget. The polarity can be reversed but this is not preferred.

The surface can be a drum, device or sheet. The surface can be a metal,ceramic or polymeric material with particularly preferred materialsselected from stainless steel, cobalt chrome, nickel titanium (nitinol)and magnesium alloys. The voltage on the power supply is increased tothe desired voltage to uniformly draw out the polymer/PTFE solution.

The applied voltage is typically from about 2,000 to 80,000 volts. Thecharge induced by the connection of the power supply repels the chargedpolymer away from the charge source and attracts them to the collectionsurface.

The collection target is preferably placed perpendicular to the pump andorifice system and is moved in at least one direction such that theentire surface is uniformly covered, with the fibers drawn towards thetarget. Once the collection surface has been adequately covered thematerial is preferably cured, sintered, and dried (which can occursimultaneously or in a series of steps), either in place, by placing theentire collection surface in an oven, or by removing the sheet tube orother form from the collection surface and sintering it in an oven.

It is well known to those skilled in the art that espin fabrics undergoshrinkage upon sintering. While not limited to any theory the shrinkageis believe to occur in two steps. Initially, the fibers and fabrics asspun contain both water and a fiberizing polymer as previouslydescribed. Upon completion of spinning the samples dry and undergo asmall degree of fiber rearrangement. At a later time the samples areheated by exposing the fibers and fabrics to temperatures of about 35°C. to about 485° C. for a period of time.

To accommodate for shrinkage, the fiber and fabrics can be spun onto anexpanded structure. The structure can then be removed or contracted.During sintering of the espin layer, the fabric shrinks to a smallersize without cracking. Another method involves spinning the fibers andfabrics onto a structure which can then be expanded and/or contractedprior to or during sintering. The range of contraction or expansion andcontraction is on the order of about 3 to 100% and depends upon thethickness and size of the electrodeposited fabric. Alternatively theespin layer can be placed upon a surface which also contracts duringsintering.

For a sheet of fabric, if the direction of the deposition is given asthe perpendicular to the plane of the fabric then contraction orexpansion/contraction must occur in at least one or more of thedirections in the plane of the fabric. For a fabric deposited upon acylindrical surface the fabric must be contracted or contracted/expandedradially and/or longitudinally. For a spherical surface the fabric mustbe contracted or contracted/expanded radially. These basic concepts ofcontraction and/or expansion/contraction can be applied to anyelectrospun fabric independent to the shape of the surface upon which itwas spun. Thus, very complex fabric shapes based upon espin fabricbecome possible.

The espin layer is preferably fibrous. Particularly preferred espinfibers have a diameter of at least 0.1μ. In a particularly preferredembodiment the product, after sintering, has fibers deposited in adensity such there is a range of distances of 0.1 to 50μ between pointsof contact.

The present disclosure can be better understood with reference to thefollowing examples.

EXAMPLES

The following general guidelines are used for the processing examplesdescribed herein of various ePTFE and espin composite constructions.

1. In espin PTFE embodiments, the viscosity of the dispersion may bechanged by the addition or removal of water from the dispersion withoutchanging the PEO to PTFE ratio.

2. A radially expanded ePTFE tube or biaxial oriented sheet is placedover a round or flat base plate to form a desired geometric shape.

3. The espin polymer layer is applied at a desired thickness, typicallyabout 0.5 to 1000 μm, onto the ePTFE or onto a surface which is thenmated to the ePTFE membrane, resulting in a composite structure.

4. If the espin coating is applied wet to the ePTFE, it is allowed todry before moving to the next process. However, if it is processed as asingle espin sheet and has dried, it will be mated to the orientedporous ePTFE layer. The mating process between the materials can berepeated multiple times until a desired multilayered composite structureis created.

5. The ePTFE/espin composite is then covered with a non-sticking releasefoil.

6. Once the composite is positioned against a base tool, pressure isapplied to the surface of the foil, thereby aiding the bonding process.

7. The composite construction is placed in an oven at temperatures ofabout 35° C. to about 485° C. to allow all materials to bond together.The bonding temperature selection is based on material selection.

8. Once the part is removed from the oven and cooled at a rate of about15 to 25 degrees per minute, it is uncovered and tested for specifiedproperties.

Example 1 Type I Construction: ePTFE/Espin PTFE

An 80μ thick stainless steel (SS) sheet 46 cm×36 cm was wrapped around arotating drum. The drum assembly was placed into a rotating chuck suchthat it was positioned to allow espinning along the entire length of theturning drum assembly.

An approximately 80,500 cPs espinning dispersion based on a mixture of4.2% (PEO/PTFE), 300,000 amu polyethylene oxide and Daikin D210 60% PTFEdispersion which had been allowed to homogenize and then turned andfiltered to achieve a smooth consistency was placed into a 10 ml plasticsyringe fitted with a 21 gauge needle. The syringe was placed into a KDScientific Model 780200L syringe pump and set to a 0.5 ml/hour pumpingrate. The needle tip was positioned at approximately 13 cm from therotating drum assembly. The rotation of the drum assembly wasapproximately 30 rpm. A traverse was used to move the espinning needlealong the length of the drum with a rate of travel of 3.0 mm/sec. Thereturn points for the traverse were set at the ends of the SS sheet. Avoltage of 10.0 kV was employed. PTFE was electrospun onto the drum for60 minutes under these conditions to yield an approximately 40μ (asdeposited post sintering) thick covering of PTFE fibers. The sheetcontaining the PTFE membrane was removed from the drum and driedovernight.

A biaxially (Biax) expanded approximately 35 cm×40 cm ePTFE sheet withan intermodal distance (IND) of 10-30μ, thickness of 34μ, and bubblepoint <3μ was placed over and centered onto a 46 cm×36 cm stainlesssteel sheet.

The SS sheet holding the dried espin PTFE membrane was then directlypositioned over the SS sheet holding the ePTFE membrane and the twosheets brought together such that the ePTFE and espin PTFE membraneswere in intimate contact. The SS foil/ePTFE/espin PTFE/SS foil structurewas then wrapped onto a 3″ ID stainless steel tube to create theassembly. The entire assembly was then wrapped in unsintered 40μ thickePTFE membrane with 5 wraps tightly applied around the entire assembly.This was then placed in an oven at 385° C. for 15.5 minutes. Sinteringtemperature and time may vary depending on the composite's thickness andbasis weight. After sintering, the assembly was removed from the ovenand placed in a cooling air box to cool for 30-60 minutes. Aftercooling, the ePTFE membrane was unwrapped and a 22 cm×28 cm portion wasremoved from the center of the espin/ePTFE composite.

Examples 2-6 Type I Construction: ePTFE/Espin PTFE

Examples 2-6 were made similarly with the modifications from Example 1and are shown in Table I. In general, the major predictor of the MeanPore Size Diameter is the ePTFE membrane IND. However, the pore size isalso affected by the pressure applied on the composite during sinteringas shown by comparison of the composite thicknesses of Examples 1 and 4with greater pressure yielding a smaller pore size. The thickness of theespin PTFE layer also has an effect as shown by Examples 1, 2, and 3with greater thickness yielding a smaller pore size.

Example 7 Type I Construction: ePTFE/Espin Polyurethane (PU)

A biaxially (Biax) expanded approximately 35 cm×40 cm ePTFE sheet withan intermodal distance (IND) of 10-30μ, thickness of 34μ, and bubblepoint <3μ was placed over and centered onto a 46 cm×36 cm stainlesssteel sheet.

An approximately 500 cPs espinning solution based on a mixture ofChronoflex AR (AdvanSource Biomaterials) (PU) 11% in a mixture of 37.5%acetone and 62.5% Dimethylacetamide was placed into a 10 ml plasticsyringe fitted with a 21 gauge needle. The syringe was placed into a KDScientific Model 780200L syringe pump and set to a 0.35 ml/hour pumpingrate. The needle tip was positioned at approximately 13 cm from therotating drum assembly. The rotation of the drum assembly wasapproximately 30 rpm. A traverse was used to move the espinning needlealong the length of the drum with a rate of travel of 3.0 mm/sec. Thereturn points for the traverse were set at the ends of the SS sheet. Avoltage of 9.2 kV was employed. PTFE was electrospun onto the drum for240 minutes under these conditions to yield an approximately 2μ thickcovering of PU fibers. The sheet containing the PTFE/PU compositemembrane was removed from the drum and dried overnight.

Example 8 Type I Construction: ePTFE/Espin Polyurethane (PU)

Example 8 was made similarly with the modifications from Example 7 shownin Table II. Again a thicker layer of the espin PU resulted in decreasedpore size.

Example 9 Type II Construction: ePTFE/Espin PTFE/ePTFE

A biaxially (Biax) expanded approximately 10 cm long ePTFE tube with anintermodal distance (IND) of 30μ, internal diameter (ID) of 4 mm, wallthickness (WT) of 0.4 mm, and porosity of 80.33% was stretched over andcentered along a 10 mm exterior diameter (OD) aluminum rod of 35 cmlength. The tube assembly was placed into a rotating chuck such that itwas positioned to allow espinning along the entire length of the turningtube assembly.

An approximately 94,000 cPs espinning dispersion based on a mixture of4.2% (PEO/PTFE), 300,000 amu polyethylene oxide and Daikin D210 60% PTFEdispersion which had been allowed to homogenize and then turned andfiltered to achieve a smooth consistency was placed into a 10 ml plasticsyringe fitted with a 16 gauge needle. The syringe was placed into aHarvard Model 702100 syringe pump and set to a 0.5 ml/hour pumping rate.The needle tip was positioned at approximately 13 cm from the rotatingtube assembly. The rotation of the tube assembly was approximately 60rpm. A traverse was used to move the espinning needle along the lengthof the tube with a rate of travel of 2.5 mm/sec. The return points forthe traverse were set at the ends of the Biax tube. A voltage of 9.3 kVwas employed. PTFE was electrospun onto the tube for 30 minutes underthese conditions to yield an approximately 20μ (as deposited postsintering) thick covering of PTFE fibers.

After allowing the tube assembly to dry overnight an ePTFE membrane ofbasis weight 8.426 g/m2 and thickness of 30μ was wrapped 6 times aroundthe tube assembly. The tube assembly was then wrapped in 80μ thickstainless steel foil followed by being further wrapped 5 times withunsintered 40μ thick ePTFE membrane applied tightly around the entireassembly. The tube assembly was then placed into an oven preheated to385° C. for 4.0 minutes. After removal from oven, cooling, andunwrapping the composite tube was determined to have a thickness of0.149 mm.

Examples 10-15 Type II Construction: ePTFE/Espin PTFE/ePTFE

Examples 10-15 were made similarly with the particulars of each Exampleshown in Table III.

Example 16 Type III Construction: Espin PTFE/ePTFE/Espin PTFE

A 40μ thick aluminum foil sheet 46 cm×6.2 cm was wrapped around arotating drum. The drum assembly was placed into a rotating chuck suchthat it was positioned to allow espinning along the entire length of theturning drum assembly.

An espinning dispersion based on a mixture of 5.2% (PEO/PTFE) 300,000amu polyethylene oxide and Daikin D210, 60% PTFE dispersion which hadbeen allowed to homogenize and then turned and filtered to achieve asmooth consistency was placed into a 10 ml plastic syringe fitted with a16 gauge needle. The syringe was placed into a KD Scientific Model780200L syringe pump and set to a 0.09 ml/hour pumping rate. The needletip was positioned at approximately 20 cm from the rotating drumassembly. The rotation of the drum assembly was approximately 30 rpm. Atraverse was used to move the espinning needle along the length of thedrum with a rate of travel of 3.0 mm/sec. The return points for thetraverse were set at the ends of the aluminum foil. A voltage of 18.0 kVwas employed. PTFE was electrospun onto the drum for 30 minutes underthese conditions to yield an approximately 80μ (as deposited postsintering) thick covering of PTFE fibers. The aluminum foil containingthe PTFE membrane was removed from the drum and dried.

After drying the green strength of the composite allowed the removal ofthe PTFE membrane from the foil and placement, centering, and loosewrapping of a 10 cm×6.5 cm portion of the PTFE membrane around a 1.0 cmexterior diameter (OD) aluminum tube twice. An ePTFE membrane:thickness—130μ, IND—12.45μ, and porosity of—51% was then wrapped 3 timesaround the espin PTFE to create a tube/espin PTFE/ePTFE assembly. Thetube assembly was placed into a rotating chuck such that it waspositioned to allow espinning along the entire length of the turningtube assembly.

An espinning dispersion based on a mixture of 5.2% (PEO/PTFE) 300,000amu polyethylene oxide and Daikin D210, 60% PTFE dispersion which hadbeen allowed to homogenize and then turned and filtered to achieve asmooth consistency was placed into a 10 ml plastic syringe fitted with a16 gauge needle. The syringe was placed into a KD Scientific Model780200L syringe pump and set to a 0.05 ml/hour pumping rate. The needletip was positioned at approximately 11.5 cm from the rotating tubeassembly. The rotation of the tube assembly was approximately 30 rpm. Atraverse was used to move the espinning needle along the length of thetube with a rate of travel of 3.0 mm/sec. The return points for thetraverse were set at the ends of the espin PTFE/ePTFE assembly. Avoltage of 16.0 kV was employed. PTFE was electrospun onto the assemblyfor 15 minutes under these conditions to yield an approximately 60μ (asdeposited post sintering) thick covering of PTFE fibers. The assemblywas removed from the drum, dried, and placed onto a fixture. Theassembly was then placed upright into an oven preheated to 385° C. for4.0 minutes.

Example 17 Type IV Construction: Substrate/Espin PTFE/ePTFE

A 40μ thick non stick aluminum foil sheet 43 cm×38 cm was wrapped arounda rotating drum. An approximately 35 cm×30 cm ePTFE sheet with a basisweight of 4.997 gsm, thickness of 7μ, and porosity of 72% was placedover, centered, and affixed onto the aluminum foil. The drum assemblywas placed into a rotating chuck such that it was positioned to allowespinning along the entire length of the turning drum assembly.

An approximately 163,000 cPs espinning dispersion based on a mixture of4.2% (PEO/PTFE), 300,000 amu polyethylene oxide and Daikin D210 60% PTFEdispersion which had been allowed to homogenize and then turned andfiltered to achieve a smooth consistency was placed into two 10 mlplastic syringes fitted with 16 gauge needles. The syringes were placedinto a KD Scientific Model 780200L syringe pump and set to a 0.75ml/hour pumping rate. The needle tips were positioned at approximately20.3 cm from the rotating drum assembly. The rotation of the drumassembly was approximately 30 rpm. A traverse was used to move theespinning needle along the length of the drum with a rate of travel of3.0 mm/sec. The return points for the traverse were set at the ends ofthe ePTFE membrane sheet. A voltage of 17.5 kV was employed. PTFE waselectrospun onto the drum for 30 minutes under these conditions to yieldan approximately 50μ (as deposited post sintering) thick covering ofPTFE fibers. The aluminum foil sheet containing the ePTFE/espin PTFEcomposite membrane was then removed from the drum and dried overnight.After drying the green strength was sufficient to allow the removal ofthe ePTFE/espin PTFE composite membrane from the foil.

A 5 cm wide section of the composite membrane was wound 3 times around a5 cm long, 0.5 cm OD porous metal tube with the espin layer in contactwith the tube. The entire assembly was then placed on a fixture, wrappedin aluminum foil and then wrapped with unsintered 40μ thick ePTFEmembrane tightly applied around the entire assembly. The assembly wasthen placed in an oven at 385° C. for 4 mins. After cooling thecomposite membrane had good appearance and adherence to the metal tube.

TABLES

TABLE I Type I: ePTFE/espin PTFE Examples PTFE Espin ePTFE ePTFEDispersion Espin PTFE/ePTFE Mean Membrane Membrane Viscosity PTFEComposite Pore Size Example Thickness IND cPs Thickness ThicknessDiameter Membrane 1.3029μ 1 34μ 10-30μ  80,500 40μ 31μ 0.5564μ 2 34μ10-30μ  80,500 50μ 31μ 0.4690μ 3 34μ 10-30μ  80,500 80μ 32μ 0.4401μ 434μ 10-30μ  87,000 40μ 30μ 0.5406μ Membrane 0.2968μ 5 23μ 2-5μ 101,00020μ 18μ 0.2915μ 6 23μ 2-5μ 105,000 30μ 22μ 0.2921μ

TABLE II Type I: ePTFE/espin PU Examples Espin ePTFE ePTFE PU EspinPTFE/ePTFE Mean Membrane Membrane Viscosity PU Composite Pore SizeExample Thickness IND cPs thickness Thickness Diameter Membrane 0.2968μ7 23μ 2-5μ 500 2μ 25μ 0.2809μ 8 23μ 2-5μ 500 1μ 24μ 0.2930μ

TABLE III Type II: ePTFE/espin PTFE/ePTFE Examples Example 9 10 11 12 1314 15 Rod 10 mm 12 mm 20 mm 20 mm 20 mm 20 mm 26 mm Diameter Tube IND30μ 40μ 40μ 40μ 40μ 40μ 40μ Tube ID 4 mm 4.1 mm 4.1 mm 4.1 mm 4.1 mm 4.1mm 4.1 mm Tube WT 0.4 mm 0.5 mm 0.5 mm 0.65 mm 0.65 mm 0.65 mm 0.65 mmTube 80.33% 78.97% 78.97% 78.97% 78.97% 78.97% 78.97% Porosity Membrane8.426 gsm 8.426 gsm 8.426 gsm 15.500 gsm 15.500 gsm 15.500 gsm 15.500gsm Basis Weight Membrane 40μ 40μ 40μ 75μ 75μ 75μ 75μ Thickness Membrane6 4 6 4 5 5 4 Layers Sintering 4 min 4 min 5 min 6 min 6.5 min 6.33 min8.33 min Time Composite 0.149 mm 0.143 mm 0.137 mm 0.185 mm 0.232 mm0.244 mm 0.220 mm Thickness

In the interests of brevity and conciseness, any ranges of values setforth in this specification are to be construed as written descriptionsupport for claims reciting any sub-ranges having endpoints which arewhole number values within the specified range in question. By way of ahypothetical illustrative example, a disclosure in this specification ofa range of 1-5 shall be considered to support claims to any of thefollowing sub-ranges: 1-4; 1-3; 1-2; 2-5; 2-4; 2-3; 3-5; 3-4; and 4-5.

These and other modifications and variations to the present disclosurecan be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present disclosure, which ismore particularly set forth in the appended claims. In addition, itshould be understood that aspects of the various embodiments can beinterchanged both in whole or in part. Furthermore, those of ordinaryskill in the art will appreciate that the foregoing description is byway of example only, and is not intended to limit the disclosure.

What is claimed is:
 1. A composite structure comprising a plurality ofnanofibers on a first surface of a first polymeric layer.
 2. Thecomposite structure of claim 1, wherein the nanofibers comprise one ofpolytetrafluoroethylene (PTFE), nylon, polyurethane, polyester,fluorinated ethylene propylene, or combinations thereof.
 3. Thecomposite structure of claim 1, wherein the plurality of nanofibers is aplurality of spun nanofibers.
 4. The composite structure of claim 3,wherein the plurality of spun nanofibers is a plurality of electrospunnanofibers.
 5. The composite structure of claim 1, wherein the firstpolymeric layer is a first layer of expanded polytetrafluoroethylene(ePTFE) and wherein the composite structure further comprises a secondePTFE layer.
 6. The composite structure of claim 5, wherein theplurality of nanofibers are sandwiched between and bind together thefirst ePTFE layer and the second ePTFE layer.
 7. A stent, comprising: afirst layer of polytetrafluoroethylene (PTFE) fibers disposed such thatit defines an outside surface of the stent; and a second layer of PTFEfibers disposed such that it defines an inside surface of the stent. 8.The stent of claim 7, wherein the surface properties of at least one ofthe layers is modulated to manipulate cellular ingrowth and response. 9.A composite structure comprising a tubular polymeric inner surface and atubular polymeric outer surface, wherein at least one of the tubularpolymeric inner surface and tubular polymeric outer surface comprises aplurality of polytetrafluoroethylene (PTFE) nanofibers.
 10. Thecomposite structure of claim 9, wherein both the tubular polymeric innersurface and tubular polymeric outer surface comprise a plurality of PTFEnanofibers.
 11. The composite structure of claim 10, wherein thepolytetrafluoroethylene (PTFE) nanofibers comprise spunpolytetrafluoroethylene (PTFE) nanofibers.
 12. The composite structureof claim 11, wherein the spun polytetrafluoroethylene (PTFE) nanofiberscomprise electrospun polytetrafluoroethylene (PTFE) nanofibers.
 13. Thecomposite structure of claim 9, further comprising a substrate and oneor more additional layers of polymeric material, wherein the one or moreadditional layers of polymeric material comprises a second plurality ofpolytetrafluoroethylene (PTFE) nanofibers.
 14. The composite structureof claim 13, wherein the one or more additional layers of polymericmaterial comprises a second plurality of electrospunpolytetrafluoroethylene (PTFE) nanofibers.
 15. The composite structureof claim 9, wherein the PTFE nanofibers have a density such that thereis a range of distances of about 0.1μ to about 50μ between points ofcontact of the nanofibers.
 16. The composite structure of claim 9,wherein the tubular polymeric inner surface and a tubular polymericouter surface have different pore sizes.